Why do leaves fall from trees in winter?

If you are used to this column, you know that only one of the three possibilities below is correct:

1) Evergreen trees grow where there is a lot of light, even in winter. When there is not enough they die, because their leaves cannot fall.

2) The sap of evergreen trees has nothing to do with that of deciduous trees : it cannot freeze! This is why they are called conifers.

3) The falling leaves, it’s a bit like the moulting of trees. If they didn’t fall, there wouldn’t be new branches in the spring, they couldn’t grow.

An oak tree pumps a minimum of 200 liters of water per day into the soil.

The correct answer is answer 2.

Yes, if the leaves fall from deciduous trees (that’s their name), it is indeed because the cellular machinery of these trees will come to a complete stop as winter approaches, in order to avoid freezing.

You’ve probably heard a thousand times that such and such a tree, or such and such a plant, did not come back in the spring, because it froze in the winter. And what freezes in a plant is the sap : by turning into ice, it expands and explodes the cells of the plant, which dies of it.

Keep in mind thata tree is an extraordinary water pump : an adult oak tree which rises to 15 or 20 meters in parks or on avenues, it is at least 200 liters of water pumped into the ground every day. And thousands of liters contained in the trunk!
This water, contained in the sap, climbs up the tree at a rate of 6 or 7 meters … per hour. It is this water and this sap that will pass into the leaves, and thanks to the sun and photosynthesis, capture the carbon in the air, and in exchange, release oxygen.

In conifers, the mechanism is the same, except that the sap is much thicker, and does not freeze, even if the temperature reaches several tens of degrees below zero. As for the foliage, which sometimes consists of needles or thorns, it is no coincidence that it has nothing to do with the leaves of other trees: it contains very very little water, and does not therefore no risk of freezing. It is also for this reason that maritime pines or umbrella pines flourish in very hot regions: their needles hardly contain water, limiting the risk of evaporation!

For the record, know that the area of ​​forests continues to increase in France. It has quite simply more than doubled in 100 years and now occupies almost a third of the French territory, and it still continues to gain ground. With agricultural land, more than 80% of our territory is green.

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